Y-Chromosome Analysis: the History of Men

What is Y-chromosome analysis? The study of Y-chromosomes reveals the history of men, from our most ancient ancestors to those who walk the earth today.

Y-chromosome analysis is a technique which uses the genetic material passed from fathers to sons. Our gender is determined by the type of chromosomes we inherit. This is how this works:

• Males have one X chromosome and one Y chromosome, while females have two X chromosomes.
• When a child is born, he or she receives one chromosome from each parent.
• A mother might pass either one of her X chromosomes to her baby.
• The father passes either his X or Y chromosome to the baby.
• If the father passes down his X chromosome, the baby will have two X chromosomes, and be a girl. If he passes down his Y chromosome, the baby will have one X and one Y chromosome, and be a boy.
• The Y chromosome is passed from father to son, virtually unchanged, enabling Y-chromosome analysis to identify family relationships between males.

Understanding Y-Chromosome Analysis

Y-chromosome analysis is often compared to the way male surnames are passed from father to son. Most of the Y-chromosome is inherited as an integral unit and passed through the generations, unaffected by maternal DNA.

Each Y-chromosome has definable segments of DNA known as markers. These markers each occur at an identifiable physical location on a chromosome known as a locus. Over time, harmless changes or mutations occur while copying Y-chromosomes at a rate of about once in every 15 to 50 generations. This makes it possible to find many Y-chromosomes descended from a common ancestor.

The Y-chromosome test uses only one type of genetic marker called a short tandem repeat (STR). Some STR basics include:

• Short tandem repeats are short sequences of repeating DNA pairs.
• These repeats are referred to as Allele.
• STR sequences usually range in length from two to four base pairs and repeat in a head-tails pattern.
• The difference between individuals is found in the variation of the frequency of these repeats.

Thomas Jefferson and the Y-chromosome

Y-chromosome analysis can be used to resolve some of history's most vigorous debates. Thomas Jefferson, the third president of the United States was thought to have possibly fathered children with Sally Hemmings who was a slave on his Virginia plantation. Blood samples taken from descendants of Hemmings' son and Jefferson's uncle confirmed this rumor as fact.

Y Chromosome Test Applications and Limitations

Y-chromosome testing is widely used in a variety of applications. These include:

• determining paternity and parental lineage
• establishing ancestral geographic and ethnic origins
• finding out if an individual is related to those with the same surname.

This type of testing also has some limitations, the most obvious being that it is only available to men. It is also important to understand that the number of markers analyzed in a specific Y-chromosome test can determine the accuracy of results.

The most basic Y-chromosome test available analyzes 12 markers of the Y-chromosome for each participant. If participants match in all 12 areas, there is a high probability that they are related. If a match is found in only one or two areas, however, the results are inconclusive. Tests analyzing an additional 25 or even 37 markers can help determine the relationship between men with much greater accuracy.

Resources

DNA Exam (n.d.). Y-Chromosome Test. Retrieved September 2, 2008 from DNA Exam Web site: http://www.800dnaexam.com/chromosome_test.aspx.

Explore DNA (n.d.). Y-Chromosome Analysis. Retrieved September 2, 2008 from Explore DNA Web site: http://www.exploredna.co.uk/y-chromosome-analysis.html.

New York Times (2008). Eugene A Foster, 81, Dies; Linked Jefferson to Slave. Retrieved from New York Times Web site: http://www.nytimes.com/2008/07/25/us/25foster.html?_r=1